class_docstr: A highly optimized equivalent of lambda x: Entmax15([x, 0]) 
code: def backward(ctx, grad_output):
      return Entmoid15._backward(ctx.saved_tensors[0], grad_output)
  
imports: from torch import nn
  from torch.autograd import Function
  import torch.nn.functional
  import torch
label_desc: Use image node_id 3 for calling the Entmoid15 obj's underlying member method code with example usage: obj.backward(ctx, grad_output) and returns: Entmoid15